System and method providing protection in the event of current sensing failure for power converter

ABSTRACT

System and method for protecting a power converter. The system includes a first comparator configured to receive a first threshold signal and a first signal and to generate a first comparison signal. The first signal is associated with an input current for a power converter. Additionally, the system includes a second comparator configured to receive a second threshold signal and the first signal and to generate a second comparison signal. The second threshold signal is different from the first threshold signal in magnitude. Moreover, the system includes a first detection component configured to receive at least the second comparison signal, detect the second comparison signal only if one or more predetermined conditions are satisfied, and generate a first detection signal based on at least information associated with the detected second comparison signal.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional No. 61/258,522,filed Nov. 5, 2009, commonly assigned, incorporated by reference hereinfor all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a control system and method forover-current protection in the event of current sensing failures. Merelyby way of example, the invention has been applied to a power converter.But it would be recognized that the invention has a much broader rangeof applicability.

Power converters are widely used for consumer electronics such asportable devices. The power converters can convert electric power fromone form to another form. As an example, the electric power istransformed from alternate current (AC) to direct current (DC), from DCto AC, from AC to AC, or from DC to DC. Additionally, the powerconverters can convert the electric power from one voltage level toanother voltage level.

The power converters include linear converters and switch-modeconverters. The switch-mode converters often use pulse-width-modulated(PWM) or pulse-frequency-modulated mechanisms. For example, a PWMswitch-mode converter is an offline flyback converter or a forwardconverter. These modulation mechanisms are usually implemented with aswitch-mode controller including various protection components. Thesecomponents can provide over-voltage protection, over-temperatureprotection, over-current protection (OCP), and over-power protection(OPP). These protections can often prevent the power converters andconnected circuitries from suffering permanent damage.

FIG. 1 is a simplified conventional switch-mode power converter withover-current protection. A switch-mode power converter 100 includes anOCP comparator 110, a PWM controller component 120, a gate driver 130, apower switch 140, resistors 150, 152, 154, and 156, a primary winding160, a secondary winding 162, an isolated feedback component 170, and aleading-edge-blanking component 192. The OCP comparator 110, the PWMcontroller component 120, the gate driver 130, and theleading-edge-blanking component 192 are parts of a chip 180 for PWMcontrol, which includes terminals 182, 184, 186 and 188. Additionally,the PWM controller component 120 includes a PWM comparator 124 and alogic controller 126. As an example, the switch-mode power converter 100is a conventional PWM flyback power converter.

As shown in FIG. 1, the PWM controller component 120 generates a PWMsignal 122, which is received by the gate driver 130. In response, thegate driver 130 sends a gate signal 132 to the power switch 140 throughthe terminal 184. Accordingly, the power switch 140 adjusts the current164 flowing through the primary winding 160. For example, if the powerswitch 140 is turned on, the power switch 140 is closed, allowing thecurrent 164 to flow through the primary winding 160. In another example,if the power switch is turned off, the power switch 140 is open, thusnot allowing the current 164 to flow through the primary winding 160.

The current 164 is sensed by the resistor 150 and converted into acurrent sensing signal 114 (e.g., V_(cs)) through the terminal 186 andthe leading-edge-blanking component 192. The current sensing signal 114is received by the OCP comparator 110 and compared with an over-currentthreshold signal 112 (e.g., V_(th) _(_) _(oc)). In response, the OCPcomparator 110 sends an over-current control signal 116 to the PWMcontroller component 120. When the current of the primary winding isgreater than a limiting level, the PWM controller component 120 turnsoff the power switch 140 and shuts down the switch-mode power converter100, thus limiting the current 164 flowing through the primary winding160 and protecting the switch-mode power converter 100.

More specifically, the output voltage of the secondary winding 162 issensed by the isolated feedback component 170. For example, the isolatedfeedback component 170 includes an error amplifier and an opto-coupler.In response, the isolated feedback component 170 sends a feedback signal123 to the PWM comparator 124 through the terminal 188. The PWMcomparator 124 also receives the current sensing signal 114 andgenerates a PWM comparator output signal 125. The PWM comparator outputsignal 125 is received by the logic controller 126, which generates thePWM signal 122 based on at least information associated with the PWMcomparator output signal 125.

FIG. 2 is a simplified diagram showing the conventional chip 180 for PWMcontrol. The chip 180 includes the OCP comparator 110, the PWMcomparator 124, the logic controller 126, the gate driver 130, theleading-edge-blanking component 192, a power-on-reset andunder-voltage-lockout component 210, an internal power supply 220, areference voltage and current generator 230, a clock and ramp signalgenerator 240, and a summation component 250. Additionally, the chip 180also includes terminals 182, 184, 186, 188, 202 and 204.

As shown in FIG. 2, under normal operation, in each cycle, the currentsensing signal 114 ramps up as the current 164 increase with time. Theramping-up slope of the current sensing signal 114 is

$\begin{matrix}{{Slope} = \frac{V_{i\; n} \times R_{s}}{L_{p}}} & ( {{Equation}\mspace{14mu} 1} )\end{matrix}$

where V_(in) represents an input voltage at a node 190, R_(s) representsthe resistance value of the resistor 150, and L_(p) represents theinductance value of the primary winding 160.

The current sensing signal 114 is added to a ramp signal 244 by thesummation component 250. The ramp signal 244 is generated by the clockand ramp signal generator 240, which also outputs a clock signal 242.The summation component 250 generates a summation signal 252, which isreceived by the PWM comparator 124. The PWM comparator 124 compares thesummation signal 252 with the feedback signal 123 and outputs the PWMcomparator output signal 125. The PWM comparator output signal 125 isreceived by the logic controller 126, which also receives a clock signal242 and the over-current control signal 116.

For example, if the PWM comparator output signal 125 is at the logic lowlevel, the summation signal 252 is larger than the feedback signal 123in magnitude, and the power switch 140 is turned off. In anotherexample, if the over-current control signal 116 is at the logic lowlevel, the current sensing signal 114 is larger than the over-currentthreshold signal 112 (e.g., V_(th) _(_) _(oc)) in magnitude, and thepower switch 140 is turned off.

FIG. 3 shows simplified conventional timing diagrams and waveforms forthe switch-mode power converter 100 where the power switch 140 is turnedoff in response to the PWM comparator output signal 125. Curves 344,342, 352, and 332 represent the signals 244, 242, 252, and 132 asfunctions of time respectively. When the summation signal 252(corresponding to the curve 352) exceeds the feedback signal 123 (e.g.,V_(FB)) in magnitude, the gate signal 132 (corresponding to the curve332) changes from the logic high level to the logic low level, causingthe power switch 140 to be turned off.

FIG. 4 shows simplified conventional timing diagrams and waveforms forthe switch-mode power converter 100 where the power switch 140 is turnedoff in response to the current sensing signal 114. Curves 444, 442, 414,and 432 represent the signals 244, 242, 114, and 132 as functions oftime respectively. When the current sensing signal 114 (corresponding tothe curve 414) exceeds the over-current threshold signal 112 (e.g.,V_(th) _(_) _(oc)) in magnitude, the gate signal 232 (corresponding tothe curve 432) changes from the logic high level to the logic low level,causing the power switch 140 to be turned off.

In more detail, the current 164 flowing through the primary winding 160is limited to:

$\begin{matrix}{I_{{ma}\; x} = \frac{V_{{th}\; \_ \; {OC}}}{R_{s}}} & ( {{Equation}\mspace{14mu} 2} )\end{matrix}$

where I_(max) is the predetermined maximum magnitude for the current164. Additionally, V_(th) _(_) _(oc) represents the magnitude of theover-current threshold signal 112, and R_(s) represents the resistancevalue of the resistor 150. As discussed above, the current sensingsignal 114 (corresponding to the curve 414) ramps up when the powerswitch 140 is turned on. If the current sensing signal 114 exceeds thepredetermined V_(th) _(_) _(oc), the over-current control signal 116changes from the logic high level to the logic low level. As a result,the power switch 140 is turned off, thus limiting the current that flowsthrough the primary winding 160 and preventing the switch-mode powerconverter 100 from being damaged by excessive current and voltagestress.

But the mechanism of over-current protection (OCP) as shown in FIGS. 1-4usually cannot function properly if the sensing of the current 164flowing through the primary winding 160 fails. For example, if theresistor 150 becomes shorted or if the terminal 186 becomes hard shortedwith zero impedance or soft shorted with very low impedance to theground, the current sensing signal 114 would become very small or nearlyzero. The current sensing signal 114 cannot accurately represent themagnitude of the current 164, thus allowing excessively large magnitudeof the current 164. The excessive current flowing through the primarywinding 160 can cause damage to the switch-mode power converter 100 dueto excessive current and voltage stress at switching or thermal run-awayat operation. For example, the excessive current can cause the primarywinding 160 to saturate. In another example, the rectifier components atthe transformer secondary side may be subject to permanent damage andeven fire due to excessively high voltage and current stress atoperation.

Hence it is highly desirable to improve the techniques of over-currentprotection (OCP).

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a control system and method forover-current protection in the event of current sensing failures. Merelyby way of example, the invention has been applied to a power converter.But it would be recognized that the invention has a much broader rangeof applicability.

According to one embodiment, a system for protecting a power converterincludes a first comparator configured to receive a first thresholdsignal and a first signal and to generate a first comparison signal. Thefirst signal is associated with an input current for a power converter.Additionally, the system includes a second comparator configured toreceive a second threshold signal and the first signal and to generate asecond comparison signal. The second threshold signal is different fromthe first threshold signal in magnitude. Moreover, the system includes afirst detection component configured to receive at least the secondcomparison signal, detect the second comparison signal only if one ormore predetermined conditions are satisfied, and generate a firstdetection signal based on at least information associated with thedetected second comparison signal. Also, the system includes a switchsignal generator coupled to at least the first detection component andconfigured to generate a switch signal for controlling a switch foradjusting the input current for the power converter based on at leastinformation associated with the first comparison signal and the firstdetection signal. The switch signal generator is further configured togenerate the switch signal to turn off the switch if the firstcomparison signal indicates the first signal is larger than the firstthreshold signal in magnitude, and the switch signal generator isfurther configured to generate the switch signal to turn off the switchif the first detection signal indicates the first signal is smaller thanthe second threshold signal in magnitude.

According to another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a firstthreshold signal and a first signal and to generate a first comparisonsignal. The first signal is associated with an input current for a powerconverter. Additionally, the system includes a second comparatorconfigured to receive a second threshold signal and the first signal andto generate a second comparison signal. The second threshold signal isdifferent from the first threshold signal in magnitude. Moreover, thesystem includes a detection and delay component configured to receive atleast the second comparison signal, detect, with or without apredetermined delay of time, the second comparison signal only if one ormore predetermined conditions are satisfied, process informationassociated with the detected second comparison signal, and generate afirst detection signal based on at least information associated with thecorresponding detected second comparison signal before the predetermineddelay of time. Also, the system includes a switch signal generatorcoupled to at least the detection and delay component and configured togenerate a switch signal for controlling a switch for adjusting theinput current for the power converter based on at least informationassociated with the first comparison signal and the first detectionsignal. The switch signal generator is further configured to generatethe switch signal to turn off the switch if the first comparison signalindicates the first signal is larger than the first threshold signal inmagnitude, and the switch signal generator is further configured togenerate the switch signal to turn off the switch if the first detectionsignal indicates the first signal is smaller than the second thresholdsignal in magnitude before the predetermined delay of time.

According to yet another embodiment, a method for protecting a powerconverter includes receiving a first signal, a first threshold signal,and a second threshold signal. The first signal is associated with aninput current for a power converter, and the second threshold signal isdifferent from the first threshold signal in magnitude. Additionally,the method includes generating a first comparison signal based on atleast information associated with the first signal and the firstthreshold signal, and generating a second comparison signal based on atleast information associated with the first signal and the secondthreshold signal. Moreover, the method includes receiving the secondcomparison signal, detecting the second comparison signal only if one ormore predetermined conditions are satisfied, generating a firstdetection signal based on at least information associated with thedetected second comparison signal, processing information associatedwith the first comparison signal and the first detection signal, andgenerating a switch signal for controlling a switch for adjusting theinput current for the power converter based on at least informationassociated with the first comparison signal and the first detectionsignal. The process for generating a switch signal for controlling aswitch includes generating the switch signal to turn off the switch ifthe first comparison signal indicates the first signal is larger thanthe first threshold signal in magnitude, and generating the switchsignal to turn off the switch if the first detection signal indicatesthe first signal is smaller than the second threshold signal inmagnitude.

According to yet another embodiment, a method for protecting a powerconverter includes receiving a first signal, a first threshold signal,and a second threshold signal. The first signal is associated with aninput current for a power converter, and the second threshold signal isdifferent from the first threshold signal in magnitude. Additionally,the method includes generating a first comparison signal based on atleast information associated with the first signal and the firstthreshold signal, generating a second comparison signal based on atleast information associated with the first signal and the secondthreshold signal, receiving the second comparison signal, detecting,with or without a predetermined delay of time, the second comparisonsignal only if one or more predetermined conditions are satisfied,processing information associated with the detected second comparisonsignal, and generating a first detection signal based on at leastinformation associated with the corresponding detected second comparisonsignal before the predetermined delay of time. Moreover, the methodincludes processing information associated with the first comparisonsignal and the first detection signal, and generating a switch signalfor controlling a switch for adjusting the input current for the powerconverter based on at least information associated with the firstcomparison signal and the first detection signal. The process forgenerating a switch signal for controlling a switch includes generatingthe switch signal to turn off the switch if the first comparison signalindicates the first signal is larger than the first threshold signal inmagnitude, and generating the switch signal to turn off the switch ifthe first detection signal indicates the first signal is smaller thanthe second threshold signal in magnitude before the predetermined delayof time.

Many benefits are achieved by way of the present invention overconventional techniques. Certain embodiments of the present inventioncan protect a switch-mode power converter even if the current sensingmechanism fails. Some embodiments of the present invention provide aprotection mechanism that limits the on-time of a power switch and thuslimit the current that flows through a primary winding, even if thecurrent sensing mechanism fails. For example, if the current sensingmechanism fails, the switch-mode power converter enters the shut downmode.

Depending upon embodiment, one or more of these benefits may beachieved. These benefits and various additional objects, features andadvantages of the present invention can be fully appreciated withreference to the detailed description and accompanying drawings thatfollow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified conventional switch-mode power converter withover-current protection.

FIG. 2 is a simplified diagram showing the conventional chip for PWMcontrol.

FIG. 3 shows simplified conventional timing diagrams and waveforms forthe switch-mode power converter where the power switch is turned off inresponse to the PWM comparator output signal.

FIG. 4 shows simplified conventional timing diagrams and waveforms forthe switch-mode power converter where the power switch is turned off inresponse to the current sensing signal.

FIG. 5 shows simplified timing diagrams and waveforms for theswitch-mode power converter where the current sensing fails and thecurrent exceeds the predetermined maximum magnitude.

FIG. 6(A) is a simplified diagram showing a switch-mode power converterwith protection according to an embodiment of the present invention.

FIG. 6(B) is a simplified diagram showing a switch-mode power converterwith protection according to another embodiment of the presentinvention.

FIG. 7(A) shows simplified timing diagrams and waveforms for theswitch-mode power converter as shown in FIG. 6(A) according to anembodiment of the present invention.

FIG. 7(B) shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIG. 6(B) according to anembodiment of the present invention.

FIG. 8(A) is a simplified diagram showing the chip for PWM control inthe switch-mode power converter as shown in FIG. 6(B) according to anembodiment of the present invention.

FIG. 8(B) is a simplified diagram showing the chip for PWM control inthe switch-mode power converter as shown in FIG. 6(B) according to anembodiment of the present invention.

FIG. 9(A) shows simplified timing diagrams and waveforms for theswitch-mode power converter as shown in FIGS. 6(B) and 8(B) under normaloperation of current sensing where the pulse width of the gate signalexceeds the pulse width of the clock signal according to an embodimentof the present invention.

FIG. 9(B) shows simplified timing diagrams and waveforms for theswitch-mode power converter as shown in FIGS. 6(B) and 8(B) under normaloperation of current sensing where the pulse width of the gate signal issmaller than the pulse width of the clock signal according to anembodiment of the present invention.

FIG. 9(C) shows simplified timing diagrams and waveforms for theswitch-mode power converter as shown in FIGS. 6(B) and 8(B) where thecurrent sensing fails and the pulse width of the gate signal exceeds thepulse width of the clock signal according to yet another embodiment ofthe present invention.

FIG. 9(D) shows simplified timing diagrams and waveforms for theswitch-mode power converter as shown in FIGS. 6(B) and 8(B) where thecurrent sensing fails after the falling edge of the clock signal and thepulse width of the gate signal exceeds the pulse width of the clocksignal according to yet another embodiment of the present invention.

FIG. 10 shows simplified timing diagrams and waveforms for theswitch-mode power converter as shown in FIGS. 6(B) and 8(B) where thecurrent sensing fails and the pulse width of the gate signal exceeds thepulse width of the clock signal according to yet another embodiment ofthe present invention.

FIG. 11 is a simplified diagram showing the chip for PWM control in theswitch-mode power converter as shown in FIG. 6(B) according to anembodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a control system and method forover-current protection in the event of current sensing failures. Merelyby way of example, the invention has been applied to a power converter.But it would be recognized that the invention has a much broader rangeof applicability.

FIG. 5 shows simplified timing diagrams and waveforms for theswitch-mode power converter 100 where the current sensing fails and thecurrent 164 exceeds the predetermined maximum magnitude. Curves 544,542, 552, 514, 532, and 564 represent the signals 244, 242, 252, 114,132, and 164 as functions of time respectively. When the current sensingfails, the current sensing signal 114 cannot accurately represent themagnitude of the current 164, thus allowing excessively large magnitudeof the current 164. Consequently, the current 164 exceeds thepredetermined maximum magnitude, and cause damage to the switch-modepower converter 100.

FIG. 6(A) is a simplified diagram showing a switch-mode power converterwith protection according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. A switch-mode powerconverter 600 includes an OCP comparator 610, a PWM comparator 624, alogic controller 626, a gate driver 630, a power switch 640, resistors650, 652, 654, and 656, a primary winding 660, a secondary winding 662,an isolated feedback component 670, a leading-edge-blanking component692, a power-on-reset and under-voltage-lockout component 710, aninternal power supply 720, a reference voltage and current generator730, a clock and ramp signal generator 740, a summation component 750, acomparator 646, a detection component 690, and a timer detectioncomponent 694.

For example, the OCP comparator 610, the PWM comparator 624, the logiccontroller 626, the gate driver 630, the leading-edge-blanking component692, the power-on-reset and under-voltage-lockout component 710, theinternal power supply 720, the reference voltage and current generator730, the clock and ramp signal generator 740, the summation component750, the comparator 646, the detection component 690, and the timerdetection component 694 are parts of a chip 680 for PWM control, whichalso includes terminals 682, 684, 686, 688, 702 and 704. In anotherexample, the PWM comparator 624 and the logic controller 626 are partsof a PWM controller component.

According to one embodiment, the OCP comparator 610, the PWM comparator624, the power switch 640, the resistors 650, 652, 654, and 656, theprimary winding 660, the secondary winding 662, the isolated feedbackcomponent 670, the leading-edge-blanking component 692, thepower-on-reset and under-voltage-lockout component 710, the internalpower supply 720, the reference voltage and current generator 730, andthe summation component 750 are substantially the same as the OCPcomparator 110, the PWM comparator 124, the power switch 140, theresistors 150, 152, 154, and 156, the primary winding 160, the secondarywinding 162, the isolated feedback component 170, theleading-edge-blanking component 192, the power-on-reset andunder-voltage-lockout component 210, the internal power supply 220, thereference voltage and current generator 230, and the summation component250 respectively.

According to another embodiment, an output voltage of the secondarywinding 662 is sensed by the isolated feedback component 670. Forexample, the isolated feedback component 670 includes an error amplifierand an opto-coupler. In another example, the isolated feedback component670 sends a feedback signal 623 to the PWM comparator 624 through theterminal 688.

In one embodiment, a current sensing signal 614 is received and added toa ramp signal 744 by the summation component 750. For example, the rampsignal 744 is generated by the clock and ramp signal generator 740,which also outputs a clock signal 742. In another example, the summationcomponent 750 generates a summation signal 752, which is also receivedby the PWM comparator 624. In another embodiment, the PWM comparator 624compares the summation signal 752 with the feedback signal 623 andoutputs the PWM comparator output signal 625.

As shown in FIG. 6(A), the PWM comparator output signal 625 is receivedby the logic controller 626, which generates a PWM signal 622 based onat least information associated with the PWM comparator output signal625. For example, the PWM signal 622 is received by the gate driver 630,and based on at least information associated with the PWM signal 622,the gate driver 630 sends a gate signal 632 to the power switch 640through the terminal 684. In another example, the power switch 640adjusts the current 664 flowing through the primary winding 660.

In one embodiment, the current 664 is sensed by the resistor 650 andconverted into the current sensing signal 614 (e.g., V_(cs)) through theterminal 686 and the leading-edge-blanking component 692. For example,the current sensing signal 614 is received by the OCP comparator 610 andcompared with an over-current threshold signal 612 (e.g., V_(th) _(_)_(oc)). In another example, in response, the OCP comparator 610 sends anover-current control signal 616 to the logic controller 626, which alsoreceives the PWM comparator output signal 625 and the clock signal 742.

As shown in FIG. 6(A), the current sensing signal 614 is also receivedby the comparator 646 and compared with a threshold signal 642 (e.g.,V_(th) _(_) _(uc)) according to one embodiment. For example, V_(th) _(_)_(uc) is much smaller than V_(th) _(_) _(oc). In another example, inresponse, the comparator 646 sends a comparison signal 644 to thedetection component 690. In yet another example, the detection component690 receives a clock signal 746 from the clock and ramp signal generator740. In one embodiment, the clock signal 746 is in sync with the clocksignal 742. For example, rising edges of the clock 746 match withfalling edges of the clock signal 742 in time. In another embodiment,the detection component 690 detects the value of the comparison signal644 at each falling edge of the clock signal 746 and/or detects thevalue of the comparison signal 644 when the clock signal 746 is at thelogic low level. For example, in response, the detection component 690generates a control signal 698 to indicate whether the comparison signal644 is at the logic high level at the falling edge or when the clocksignal 746 is at the logic low level.

According to one embodiment, the logic controller 626 receives thecontrol signal 698, the over-current control signal 616, the PWMcomparator output signal 625, and the clock signal 742. For example, thelogic controller 626, in response, generates the PWM signal 622 based onat least information associated with the signals 698, 616, 625, and 742.According to another embodiment, the PWM signal 622 is received by thegate driver 630, which outputs the gate signal 632 to the power switch640 through the terminal 684.

For example, if the PWM comparator output signal 625 is at the logic lowlevel and the summation signal 752 is larger than the feedback signal623 in magnitude, the power switch 640 is turned off. In anotherexample, if the over-current control signal 616 is at the logic lowlevel and the current sensing signal 614 is larger than the over-currentthreshold signal 612 (e.g., Vth_oc) in magnitude, the power switch 640is turned off and the switch-mode power converter 600 is shut down tolimit the magnitude of the current 664 and protect the switch-mode powerconverter 600. In yet another example, if the control signal 698indicates that the comparison signal 644 is at the logic high level atthe falling edge, the power switch 640 is turned off.

In one embodiment, the control signal 698 is also received by the timerdetection component 694, which generates a control signal 696 thatindicates whether the control signal 698 keeps indicating the comparisonsignal 644 is at the logic high level at the falling edges for apredetermined period of time. For example, the control signal 696 isreceived by the gate driver 630. In another example, if the controlsignal 644 keeps indicating the comparison signal 644 is at the logichigh level at the falling edges for the predetermined period of time,the gate signal 632 causes the switch-mode power converter 600 to shutdown in order to limit the current 664 and protect the switch-mode powerconverter 600.

As discussed above and further emphasized here, FIG. 6(A) is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the control signal 698 is not receivedby the logic controller 626, and the timer detection component 694 isreplaced by a delay component, which, upon receipt of the control signal698, causes the switch-mode power converter 600 to shut down, as shownin FIG. 6(B).

FIG. 6(B) is a simplified diagram showing a switch-mode power converterwith protection according to another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. Aswitch-mode power converter 600 includes an OCP comparator 610, a PWMcomparator 624, a logic controller 627, a gate driver 630, a powerswitch 640, resistors 650, 652, 654, and 656, a primary winding 660, asecondary winding 662, an isolated feedback component 670, aleading-edge-blanking component 692, a power-on-reset andunder-voltage-lockout component 710, an internal power supply 720, areference voltage and current generator 730, a clock and ramp signalgenerator 740, a summation component 750, a comparator 646, a detectioncomponent 690, and a delay component 695.

For example, the OCP comparator 610, the PWM comparator 624, the logiccontroller 627, the gate driver 630, the leading-edge-blanking component692, the power-on-reset and under-voltage-lockout component 710, theinternal power supply 720, the reference voltage and current generator730, the clock and ramp signal generator 740, the summation component750, the comparator 646, the detection component 690, and the delaycomponent 695 are parts of a chip 680 for PWM control, which alsoincludes terminals 682, 684, 686, 688, 702 and 704. In another example,the PWM comparator 624 and the logic controller 627 are parts of a PWMcontroller component.

According to one embodiment, the OCP comparator 610, the PWM comparator624, the logic controller 627, the power switch 640, the resistors 650,652, 654, and 656, the primary winding 660, the secondary winding 662,the isolated feedback component 670, the leading-edge-blanking component692, the power-on-reset and under-voltage-lockout component 710, theinternal power supply 720, the reference voltage and current generator730, and the summation component 750 are substantially the same as theOCP comparator 110, the PWM comparator 124, the logic controller 126,the power switch 140, the resistors 150, 152, 154, and 156, the primarywinding 160, the secondary winding 162, the isolated feedback component170, the leading-edge-blanking component 192, the power-on-reset andunder-voltage-lockout component 210, the internal power supply 220, thereference voltage and current generator 230, and the summation component250 respectively.

According to another embodiment, the PWM comparator output signal 625 isreceived by the logic controller 627, which also receives theover-current control signal 616 and the clock signal 742. For example,the logic controller 627, in response, generates the PWM signal 699based on at least information associated with the signals 616, 625, and742. In another example, the PWM signal 699 is received by the gatedriver 630.

As shown in FIG. 6(B), the control signal 698 is received by the delaycomponent 695, which, after a predetermined delay, generates a controlsignal 697. For example, the control signal 697 is the same as thecorresponding control signal 698 before the predetermined delay. Inanother example, the control signal 697 is received by the gate driver630.

In one embodiment, the gate driver 630 receives the control signal 697and the PWM signal 699, and in response, outputs the gate signal 632 tothe power switch 640 through the terminal 684. For example, the powerswitch 640 adjusts the current 664 flowing through the primary winding660. In another example, if the control signal 697 indicates thecomparison signal 644 is at the logic high level at the falling edge ofthe clock signal 746, the gate signal 632 causes the switch-mode powerconverter 600 to shut down in order to limit the current 664 and protectthe switch-mode power converter 600.

FIG. 7(A) shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIG. 6(A) according to anembodiment of the present invention. These diagrams and waveforms aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications.

As shown in FIG. 7(A), curves 844, 842, 846, 814, 832, and 864 representthe signals 744, 742, 746, 614, 632, and 664 as functions of timerespectively. According to one embodiment, if the current sensing fails,the current sensing signal 614 (corresponding to the curve 814) remainsnearly zero or very small in magnitude. For example, the current sensingsignal 614 (corresponding to the curve 814) is received by thecomparator 646 and compared with the threshold signal 642 (e.g., V_(th)_(_) _(uc)), which is smaller than the over-current threshold signal 612(e.g., Vth_oc) in magnitude. In another example, at falling edges of theclock signal 746 and when the clock signal 746 is at the logic low level(corresponding to the curve 846), the comparison signal 644 from thecomparator 646 is detected by the detection component 690. In oneembodiment, if, at a falling edge of the clock signal 746, thecomparison signal 644 is at the logic high level, the power switch 640is turned off and the on-time of the power switch 640 is limited to thepulse width (e.g., T_(a)) of the clock signal 746 (corresponding to thecurve 846). For example, the pulse width (e.g., T_(a)) of the clocksignal 746 is chosen to correspond to 10%-30% of the duty cycle of themaximum switching frequency. In another example, the duty cycle of thegate signal 632 is limited to the duty cycle of the clock signal 746,and the current 664, under the discontinuous current mode (DCM), islimited:

$\begin{matrix}{I_{limit} = {\frac{V_{i\; n}}{L_{p}}T_{a}}} & ( {{Equation}\mspace{14mu} 3} )\end{matrix}$

where V_(in) is the line input voltage at node 690, and L_(p) is theinductance of the primary winding 660. In another embodiment, if thecomparison signal 644 is detected to be at the logic high level for apredetermined period of time (e.g., T_(b)), the switch-mode powerconverter 600 or the power switch 640 is shut down. For example, theswitch-mode power converter 600 is shut down by turning off the powerswitch 640 until a reset signal is received. In another example, thepower switch 640 is shut down by turning off the power switch 640 untila reset signal is received.

FIG. 7(B) shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIG. 6(B) according to anembodiment of the present invention. These diagrams and waveforms aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications.

As shown in FIG. 7(B), curves 845, 843, 847, 815, 833, and 865 representthe signals 744, 742, 746, 614, 632, and 664 as functions of timerespectively. For example, the curves 845, 843, 847, 815, 833, and 865are similar with the curves 844, 842, 846, 814, 832, and 864respectively, except that in FIG. 7(B), if the comparison signal 644 isonce detected to be at the logic high level, the switch-mode powerconverter 600 or the power switch 640 is shut down as shown by the curve833 with a predetermined delay that is equal to zero. For example, theswitch-mode power converter 600 is shut down by turning off the powerswitch 640 until a reset signal is received. In another example, thepower switch 640 is shut down by turning off the power switch 640 untila reset signal is received.

FIG. 8(A) is a simplified diagram showing the chip 680 for PWM controlin the switch-mode power converter 600 as shown in FIG. 6(B) accordingto an embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The chip 680 for PWM control includes at least theOCP comparator 610, the PWM comparator 624, the gate driver 630, theleading-edge-blanking component 692, the summation component 750, thecomparator 646, a flip-flop component 1626, AND gates 1627 and 1690, aNOT gate 1691, a deglitch component 1694, and a latch component 1695.Additionally, the chip 680 also includes at least the terminals 684, 686and 688.

Referring to FIG. 6(B), the logic controller 627 includes the flip-flopcomponent 1626 and the AND gate 1627 according to one embodiment.According to another embodiment, the detection component 690 includesthe AND gate 1690 and the NOT gate 1691. According to yet anotherembodiment, the delay component 695 includes the deglitch component 1694and the latch component 1695.

As shown in FIG. 8(A), the comparison signal 644 is detected at eachfalling edge of the clock signal 746 and when the clock signal 746 is atthe logic low level according to one embodiment. For example, undernormal operation for current sensing, when the power switch 640 is justturned on, the comparison signal 644 is at the logic high level as thecurrent 664 ramps up. In another example, if the current sensing signal614 reaches or exceeds the threshold signal 642 (e.g., V_(th) _(_)_(uc)) before the falling edge of the clock signal 746, the comparisonsignal 644 changes to the logic low level before the falling edge of theclock signal 746. Consequently, according to one embodiment, an outputsignal 1692 of the AND gate 1690 is also at the logic low level, asfollows:

$\begin{matrix}{V_{{th}\; \_ \; {UC}} < {\frac{V_{i\; n}}{L_{p}} \times R_{s} \times T_{a}}} & ( {{Equation}\mspace{14mu} 4} )\end{matrix}$

where V_(in) represents an input voltage at a node 690, L_(p) representsthe inductance value of the primary winding 660, R_(s) represents theresistance value of the resistor 650, and T_(a) represents the pulsewidth of the clock signal 746.

Therefore, the current 664, under the discontinuous current mode (DCM),is, for example, limited according to Equation 3. In yet anotherexample, if the current sensing fails, the current sensing signal 614remains nearly zero or very small in magnitude; therefore, thecomparison signal 644 remains at the logic high level after the pulsewidth of the clock signal 746, and the output signal 1692 is also at thelogic high level.

According to one embodiment, the signal 1692 is received by the deglitchcomponent 1694, which, with a predetermined delay, outputs a signal 1696to the latch component 1695. For example, the signal 1696 is the same asthe corresponding signal 1692 before the predetermined delay. In anotherexample, in response, the latch component 1695 outputs a signal 1698 tothe gate driver 630. In one embodiment, if the signal 1692 is at thelogic low level, the corresponding signal 1698 is at the logic highlevel. In another embodiment, if the signal 1692 is at the logic highlevel, the corresponding signal 1698 is at the logic low level. As shownin FIG. 8(A), if the signal 1698 is at the logic low level, the gatesignal 632 is also at the logic low level, causing the power switch 640to be turned off and the switch-mode power converter to be shut down.

FIG. 8(B) is a simplified diagram showing the chip 680 for PWM controlin the switch-mode power converter 600 as shown in FIG. 6(B) accordingto an embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications.

The chip 680 for PWM control includes at least the OCP comparator 610,the PWM comparator 624, the gate driver 630, the leading-edge-blankingcomponent 692, the summation component 750, a comparator 1646, aflip-flop component 1626, an AND gate 1627, a NOR gate 1680, a NOT gate1681, a deglitch component 1694, and a latch component 1695.Additionally, the chip 680 also includes at least the terminals 684, 686and 688.

Referring to FIG. 6(B), the logic controller 626 includes the flip-flopcomponent 1626 and the AND gate 1627 according to one embodiment.According to another embodiment, the detection component 690 includesthe NOR gate 1680 and the NOT gate 1681. According to yet anotherembodiment, the delay component 695 includes the deglitch component 1694and the latch component 1695.

In comparison between FIG. 8(A) and FIG. 8(B), the comparator 646, theNOT gate 1691 and the AND gate 1690 are replaced by the comparator 1646,the NOT gate 1681 and the NOR gate 1680 respectively according to oneembodiment. For example, as shown in FIG. 8(B), the comparator 1646receives the threshold signal 642 (e.g., V_(th) _(_) _(uc)) at the “−”terminal and the current sensing signal 614 at the “+” terminal and inresponse generates a comparison signal 1644 to the NOR gate 1680.

FIG. 9(A) shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIGS. 6(B) and 8(B) undernormal operation of current sensing where the pulse width of the gatesignal 632 exceeds the pulse width of the clock signal 746 according toan embodiment of the present invention. These diagrams and waveforms aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications.

As shown in FIG. 9(A), curves 942, 922, 914, and 1944 represent thesignals 742, 632, 614, and 1644 as functions of time respectively, and acurve 946 represents the inverted version of the signal 746 as afunction of time, if the current sensing mechanism operates normally andthe pulse width of the gate signal 632 (corresponding to the curve 922)exceeds the pulse width of the clock signal 746 (corresponding to thecurve 946). For example, the logic high level of the curve 946corresponds to the logic low level of the signal 746, and the logic lowlevel of the curve 946 corresponds to the logic high level of the signal746.

In another example, at a rising edge of the clock signal 742(corresponding to the curve 942), the gate signal 632 (corresponding tothe curve 922) changes from the logic low level to the logic high leveland causes the power switch 640 to be turned on, but the signal 1644(corresponding to the curve 1944) remains at the logic low level. In yetanother example, with the increase of the current sensing signal 614(corresponding to the curve 914), the signal 1644 (corresponding to thecurve 1944) changes from the logic low level to the logic high level. Inyet another example, at the falling edge of the clock signal 746 andwhen the clock signal 746 is at the logic low level (corresponding tothe curve 946), if the gate signal 632 (corresponding to the curve 922)remains at the logic high level, the signal 1644 (corresponding to thecurve 1944) is detected to be at the logic high level and the sensingoperation is determined to be normal.

FIG. 9(B) shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIGS. 6(B) and 8(B) undernormal operation of current sensing where the pulse width of the gatesignal 632 is smaller than the pulse width of the clock signal 746according to an embodiment of the present invention. These diagrams andwaveforms are merely examples, which should not unduly limit the scopeof the claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

As shown in FIG. 9(B), curves 1942, 1922, 1914, and 2944 represent thesignals 742, 632, 614, and 1644 as functions of time respectively, and acurve 1946 represents the inverted version of the signal 746 as afunction of time, if the current sensing mechanism operates normally andthe pulse width of the gate signal 632 (corresponding to the curve 1922)is smaller than the pulse width of the clock signal 746 (correspondingto the curve 1946). For example, the logic high level of the curve 1946corresponds to the logic low level of the signal 746, and the logic lowlevel of the curve 1946 corresponds to the logic high level of thesignal 746.

In another example, at a rising edge of the clock signal 742(corresponding to the curve 1942), the gate signal 632 (corresponding tothe curve 1922) changes from the logic low level to the logic high leveland causes the power switch 640 to be turned on, but the signal 1644(corresponding to the curve 2944) remains at the logic low level. In yetanother example, with the increase of the current sensing signal 614(corresponding to the curve 1914), the signal 1644 (corresponding to thecurve 2944) changes from the logic low level to the logic high level. Inyet another example, at the falling edge of the clock signal 746 andwhen the clock signal 746 is at the logic low level (corresponding tothe curve 1946), if the gate signal 632 (corresponding to the curve1922) is at the logic low level, the signal 1644 (corresponding to thecurve 2944) is not detected and whether the current sensing mechanism isnormal is not assessed.

According to one embodiment, if the pulse width of the gate signal 632(corresponding to the curve 1922) is smaller than the pulse width of theclock signal 746 (corresponding to the curve 1946), regardless ofwhether the current sensing mechanism is normal or not, the current 664should not become so large as to cause significant damage to theswitch-mode power converter 600.

FIG. 9(C) shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIGS. 6(B) and 8(B) wherethe current sensing fails and the pulse width of the gate signal 632exceeds the pulse width of the clock signal 746 according to yet anotherembodiment of the present invention. These diagrams and waveforms aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications.

As shown in FIG. 9(C), curves 2942, 2922, 2914, and 3944 represent thesignals 742, 632, 614, and 1644 as functions of time respectively, and acurve 2946 represents the inverted version of the signal 746 as afunction of time, if the current sensing mechanism fails and the pulsewidth of the gate signal 632 (corresponding to the curve 2922) exceedsthe pulse width of the clock signal 746 (corresponding to the curve2946). For example, the logic high level of the curve 2946 correspondsto the logic low level of the signal 746, and the logic low level of thecurve 2946 corresponds to the logic high level of the signal 746.

In another example, at a rising edge of the clock signal 742(corresponding to the curve 2942), the gate signal 632 (corresponding tothe curve 2922) changes from the logic low level to the logic high leveland causes the power switch 640 to be turned on, but the signal 1644(corresponding to the curve 3944) remains at the logic low level. In yetanother example, if the current sensing fails, the current sensingsignal 614 (corresponding to the curve 2914) remains nearly zero or verysmall in magnitude and the signal 1644 (corresponding to the curve 3944)remains at the logic low level. In yet another example, at the fallingedge of the clock signal 746 and when the clock signal 746 is at thelogic low level (corresponding to the curve 2946), if the gate signal632 (corresponding to the curve 2922) is at the logic high level, thesignal 1644 (corresponding to the curve 3944) is detected to be at thelogic low level and the current sensing mechanism is determined to havefailed. In response, the gate signal 632 (corresponding to the curve2922) changes to the logic low level and shut down the switch-mode powerconverter after a predetermined delay (e.g., T_(delay)).

FIG. 9(D) shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIGS. 6(B) and 8(B) wherethe current sensing fails after the falling edge of the clock signal 746and the pulse width of the gate signal 632 exceeds the pulse width ofthe clock signal 746 according to yet another embodiment of the presentinvention. These diagrams and waveforms are merely examples, whichshould not unduly limit the scope of the claims. One of ordinary skillin the art would recognize many variations, alternatives, andmodifications.

As shown in FIG. 9(D), curves 3942, 3922, 3914, and 4944 represent thesignals 742, 632, 614, and 1644 as functions of time respectively, and acurve 3946 represents the inverted version of the signal 746 as afunction of time, if the current sensing mechanism fails after thefalling edge of the clock signal 746 (corresponding to the curve 3946)and the pulse width of the gate signal 632 (corresponding to the curve3922) exceeds the pulse width of the clock signal 746 (corresponding tothe curve 3946). For example, the logic high level of the curve 3946corresponds to the logic low level of the signal 746, and the logic lowlevel of the curve 3946 corresponds to the logic high level of thesignal 746.

In another example, at a rising edge of the clock signal 742(corresponding to the curve 3942), the gate signal 632 (corresponding tothe curve 3922) changes from the logic low level to the logic high leveland causes the power switch 640 to be turned on, but the signal 1644(corresponding to the curve 4944) remains at the logic low level. In yetanother example, if the current sensing fails after the falling edge ofthe clock signal 746 (corresponding to the curve 3946), the currentsensing signal 614 (corresponding to the curve 3914) becomes nearly zeroor very small in magnitude when the clock signal 746 is at the logic lowlevel (corresponding to the curve 3946). At that time, if the gatesignal 632 (corresponding to the curve 3922) is at the logic high level,the signal 1644 (corresponding to the curve 4944) is detected to be atthe logic low level and the current sensing mechanism is determined tohave failed according to one embodiment. In response, for example, thegate signal 632 (corresponding to the curve 3922) changes to the logiclow level and shut down the switch-mode power converter after apredetermined delay (e.g., T_(delay)).

As discussed above and further emphasized here, FIGS. 8(A) and (B) aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications. For example, the threshold signal 642(e.g., V_(th) _(_) _(uc)) changes with time and is in sync with the rampsignal 744. In another example, the ramping slope of the thresholdsignal 642 (e.g., V_(th) _(_) _(uc)) is predetermined so that the normaloperation at low AC input (e.g., VAC) is not be affected.

FIG. 10 shows simplified timing diagrams and waveforms for theswitch-mode power converter 600 as shown in FIGS. 6(B) and 8(B) wherethe current sensing fails and the pulse width of the gate signal 632exceeds the pulse width of the clock signal 746 according to yet anotherembodiment of the present invention. These diagrams and waveforms aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications.

As shown in FIG. 10, curves 2044, 1042, 1022, 1042, and 1044 representthe signals 744, 742, 632, 642, and 1644 as functions of timerespectively, and a curve 1046 represents the inverted version of thesignal 746 as a function of time, if the current sensing mechanism failsand the pulse width of the gate signal 632 (corresponding to the curve1022) exceeds the pulse width of the clock signal 746 (corresponding tothe curve 1046). For example, the logic high level of the curve 1046corresponds to the logic low level of the signal 746, and the logic lowlevel of the curve 1046 corresponds to the logic high level of thesignal 746.

In another example, the threshold signal 642 (e.g., V_(th) _(_) _(uc))(corresponding to the curve 1042) changes with time and is in sync withthe ramp signal 744 (corresponding to the curve 2044). In yet anotherexample, at a rising edge of the signal 742 (corresponding to the curve1042), the gate signal 632 (corresponding to the curve 1022) changesfrom the logic low level to the logic high level and causes the powerswitch 640 to be turned on, but the signal 1644 (corresponding to thecurve 1044) remains at the logic low level. In another example, if thecurrent sensing fails, the current sensing signal 614 remains nearlyzero or very small in magnitude and the signal 1644 (corresponding tothe curve 1044) remains at the logic low level. In yet another example,at the falling edge of the clock signal 746 and when the clock signal746 is at the logic low level (corresponding to the curve 1046), if thegate signal 632 (corresponding to the curve 1022) is at the logic highlevel, the signal 1644 (corresponding to the curve 1044) is detected tobe at the logic low level and the current sensing mechanism isdetermined to have failed. In response, the gate signal 632(corresponding to the curve 1022) changes to the logic low level andshut down the switch-mode power converter after a predetermined delay(e.g., T_(delay)).

According to another embodiment, if the current sensing mechanismoperates normally and the pulse width of the gate signal 632 exceeds thepulse width of the clock signal 746, the current sensing signal 614 isgreater than the threshold signal 642 (e.g., V_(th) _(_) _(uc)) whichchanges with time and is in sync with the ramp signal 744. For example,as shown in FIG. 8(B), the comparison signal 1644 remains at the logichigh level, and the current sensing mechanism is determined to benormal.

As discussed above and further emphasized here, FIG. 6 (B) is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, a subcomponent of the detectioncomponent 690 outputs a signal to a subcomponent of the delay component695. In response, the subcomponent of the delay component 695 sendsanother signal to another subcomponent of the detection component 690,which outputs yet another signal to another subcomponent of the delaycomponent 695, as shown in FIG. 11.

FIG. 11 is a simplified diagram showing the chip 680 for PWM control inthe switch-mode power converter 600 as shown in FIG. 6(B) according toan embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The chip 680 for PWM control includes at least theOCP comparator 610, the PWM comparator 624, the gate driver 630, theleading-edge-blanking component 692, the summation component 750, thecomparator 646, the flip-flop component 1626, the AND gate 1627, an ANDgate 1190, a NOT gate 1191, a flip-flop component 1120, a deglitchcomponent 1194, a latch component 1195, and a timer component 1110.Additionally, the chip 680 also includes at least the terminals 684, 686and 688.

Referring to FIG. 6(B), the logic controller 627 includes the flip-flopcomponent 1626 and the AND gate 1627 according to one embodiment.According to another embodiment, the detection component 690 includesthe AND gate 1190, the NOT gate 1191, and the flip-flop component 1120.According to yet another embodiment, the delay component 695 includesthe deglitch component 1194, the latch component 1195 and a timercomponent 1110.

As shown in FIG. 11, when the power switch 640 is just turned on, thecomparison signal 644 is at the logic high level as the current 664ramps up. For example, under normal operation for current sensing, thecomparison signal 644 changes to the logic low level before the fallingedge of the clock signal 746 if the current sensing signal 614 reachesor exceeds the threshold signal 642 (e.g., V_(th) _(_) _(uc)) alsobefore the falling edge of the clock signal 746. In another example, ifthe current sensing fails, the current sensing signal 614 remains nearlyzero or very small in magnitude even though the current 664 ramps up;therefore, the comparison signal 644 remains at the logic high leveleven after the pulse width of the clock signal 746.

In one embodiment, the comparison signal 644 is received by the AND gate1190, which also receives an output signal 1628 from the AND gate 1627and in response generates a signal 1192. For example, the signal 1192 isreceived by the deglitch component 1194, which, with a predetermineddelay, outputs a signal 1196 to the flip-flop component 1120. In anotherexample, the signal 1196 is the same as the corresponding signal 1192before the predetermined delay.

In yet another example, the flip-flop component 1120 also receives theclock signal 746 and a signal 1124 from the NOT gate 1191, which alsoreceives the clock signal 742. In yet another example, at each fallingedge of the clock signal 746, the flip-flop component 1120 generates anoutput signal 1122 that is equal to the value of the signal 1196 at thefalling edge of the clock signal 746.

In another embodiment, the signal 1122 is received by the latchcomponent 1195. For example, in response, the latch component 1195outputs a signal 1198 to the gate driver 630. In another example, if theoutput signal 1122 is at the logic low level, the corresponding signal1198 is at the logic high level. In yet another example, if the signal1122 is at the logic high level, the corresponding signal 1198 is at thelogic low level. In yet another embodiment, if the signal 1198 is at thelogic low level, the gate signal 632 is also at the logic low level,causing the power switch 640 to be turned off.

As shown in FIG. 11, the signal 1198 is also received by the timercomponent 1110. For example, if the timer component 1110 receives thesignal 1198 at the logic low level, the timer component 1110 would resetthe signal 1198 to the logic high level after a predetermined period oftime, and the signal 1198 at the logic high level would cause the powerswitch 640 to be ready and/or enabled to turn on again, for example, innext clock cycle. In another example, the power switch 640 is turned offagain if the signal 1198 changes to the logic low level in response tothe corresponding signal 1122. According to another embodiment, the chip680 as shown in FIG. 11 detects whether the current sensing mechanismoperates normally at falling edges of the clock signal 746, not when theclock signal 746 stays at the logic low level.

As discussed above and further emphasized here, FIG. 11 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the timer component 1110 is removed.Without the timer component 1110, if the signal 1198 is at the logic lowlevel, the gate signal 632 is also at the logic low level, causing thepower switch 640 to be turned off and the switch-mode power converter tobe shut down according to one embodiment.

According to another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a firstthreshold signal and a first signal and to generate a first comparisonsignal. The first signal is associated with an input current for a powerconverter. Additionally, the system includes a second comparatorconfigured to receive a second threshold signal and the first signal andto generate a second comparison signal. The second threshold signal isdifferent from the first threshold signal in magnitude. Moreover, thesystem includes a first detection component configured to receive atleast the second comparison signal, detect the second comparison signalonly if one or more predetermined conditions are satisfied, and generatea first detection signal based on at least information associated withthe detected second comparison signal. Also, the system includes aswitch signal generator coupled to at least the first detectioncomponent and configured to generate a switch signal for controlling aswitch for adjusting the input current for the power converter based onat least information associated with the first comparison signal and thefirst detection signal. The switch signal generator is furtherconfigured to generate the switch signal to turn off the switch if thefirst comparison signal indicates the first signal is larger than thefirst threshold signal in magnitude, and the switch signal generator isfurther configured to generate the switch signal to turn off the switchif the first detection signal indicates the first signal is smaller thanthe second threshold signal in magnitude. For example, the system isimplemented according to FIG. 6(A).

According to another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a firstthreshold signal and a first signal and to generate a first comparisonsignal. The first signal is associated with an input current for a powerconverter. Additionally, the system includes a second comparatorconfigured to receive a second threshold signal and the first signal andto generate a second comparison signal. The second threshold signal isdifferent from the first threshold signal in magnitude. Moreover, thesystem includes a detection and delay component configured to receive atleast the second comparison signal, detect, with or without apredetermined delay of time, the second comparison signal only if one ormore predetermined conditions are satisfied, process informationassociated with the detected second comparison signal, and generate afirst detection signal based on at least information associated with thecorresponding detected second comparison signal before the predetermineddelay of time. Also, the system includes a switch signal generatorcoupled to at least the detection and delay component and configured togenerate a switch signal for controlling a switch for adjusting theinput current for the power converter based on at least informationassociated with the first comparison signal and the first detectionsignal. The switch signal generator is further configured to generatethe switch signal to turn off the switch if the first comparison signalindicates the first signal is larger than the first threshold signal inmagnitude, and the switch signal generator is further configured togenerate the switch signal to turn off the switch if the first detectionsignal indicates the first signal is smaller than the second thresholdsignal in magnitude before the predetermined delay of time. For example,the system is implemented according to FIG. 6(B), FIG. 8(A), FIG. 8(B),and/or FIG. 11.

In another example, as shown in FIG. 8(A) and/or FIG. 8(B), thedetection and delay component is further configured to receive at leastthe second comparison signal, detect without the predetermined delay oftime the second comparison signal only if the one or more predeterminedconditions are satisfied, delay the detected second comparison signal bythe predetermined delay of time, and generate a first detection signalbased on at least information associated with the corresponding delayeddetected second comparison signal before the predetermined delay oftime. In yet another example, as shown in FIG. 11, the detection anddelay component is configured to receive at least the second comparisonsignal, detect with the predetermined delay of time the secondcomparison signal only if the one or more predetermined conditions aresatisfied, process information associated with the detected delayedsecond comparison signal, and generate a first detection signal based onat least information associated with the corresponding detected delayedsecond comparison signal before the predetermined delay of time.

According to yet another embodiment, a method for protecting a powerconverter includes receiving a first signal, a first threshold signal,and a second threshold signal. The first signal is associated with aninput current for a power converter, and the second threshold signal isdifferent from the first threshold signal in magnitude. Additionally,the method includes generating a first comparison signal based on atleast information associated with the first signal and the firstthreshold signal, and generating a second comparison signal based on atleast information associated with the first signal and the secondthreshold signal. Moreover, the method includes receiving the secondcomparison signal, detecting the second comparison signal only if one ormore predetermined conditions are satisfied, generating a firstdetection signal based on at least information associated with thedetected second comparison signal, processing information associatedwith the first comparison signal and the first detection signal, andgenerating a switch signal for controlling a switch for adjusting theinput current for the power converter based on at least informationassociated with the first comparison signal and the first detectionsignal. The process for generating a switch signal for controlling aswitch includes generating the switch signal to turn off the switch ifthe first comparison signal indicates the first signal is larger thanthe first threshold signal in magnitude, and generating the switchsignal to turn off the switch if the first detection signal indicatesthe first signal is smaller than the second threshold signal inmagnitude. For example, the method is implemented according to FIG.6(A).

According to yet another embodiment, a method for protecting a powerconverter includes receiving a first signal, a first threshold signal,and a second threshold signal. The first signal is associated with aninput current for a power converter, and the second threshold signal isdifferent from the first threshold signal in magnitude. Additionally,the method includes generating a first comparison signal based on atleast information associated with the first signal and the firstthreshold signal, generating a second comparison signal based on atleast information associated with the first signal and the secondthreshold signal, receiving the second comparison signal, detecting,with or without a predetermined delay of time, the second comparisonsignal only if one or more predetermined conditions are satisfied,processing information associated with the detected second comparisonsignal, and generating a first detection signal based on at leastinformation associated with the corresponding detected second comparisonsignal before the predetermined delay of time. Moreover, the methodincludes processing information associated with the first comparisonsignal and the first detection signal, and generating a switch signalfor controlling a switch for adjusting the input current for the powerconverter based on at least information associated with the firstcomparison signal and the first detection signal. The process forgenerating a switch signal for controlling a switch includes generatingthe switch signal to turn off the switch if the first comparison signalindicates the first signal is larger than the first threshold signal inmagnitude, and generating the switch signal to turn off the switch ifthe first detection signal indicates the first signal is smaller thanthe second threshold signal in magnitude before the predetermined delayof time. For example, the method is implemented according to FIG. 6(B),FIG. 8(A), FIG. 8(B), and/or FIG. 11.

In another example, as shown in FIG. 8(A) and/or FIG. 8(B), the processfor detecting, with or without a predetermined delay of time, the secondcomparison signal includes detecting, without the predetermined delay oftime, the second comparison signal only if the one or more predeterminedconditions are satisfied. Additionally, as shown in FIG. 8(A) and/orFIG. 8(B), the process for processing information associated with thedetected second comparison signal includes delaying the detected secondcomparison signal by the predetermined delay of time, and the processfor generating a first detection signal includes generating the firstdetection signal based on at least information associated with thecorresponding delayed detected second comparison signal before thepredetermined delay of time according to one embodiment.

In yet another example, as shown in FIG. 11, the process for detecting,with or without a predetermined delay of time, the second comparisonsignal includes detecting with the predetermined delay of time thesecond comparison signal only if the one or more predeterminedconditions are satisfied. Moreover, as shown in FIG. 11, the process forprocessing information associated with the detected second comparisonsignal includes processing information associated with the detecteddelayed second comparison signal, and the process for generating a firstdetection signal includes generating the first detection signal based onat least information associated with the corresponding detected delayedsecond comparison signal before the predetermined delay of timeaccording to another embodiment.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1. A system for protecting a power converter, the system comprising: afirst comparator configured to receive a first threshold signal and afirst signal and to generate a first comparison signal, the first signalbeing associated with an input current for a power converter; a secondcomparator configured to receive a second threshold signal and the firstsignal and to generate a second comparison signal, the second thresholdsignal being different from the first threshold signal in magnitude; afirst detection component configured to receive at least the secondcomparison signal, detect the second comparison signal only if one ormore predetermined conditions are satisfied, and generate a firstdetection signal based on at least information associated with thedetected second comparison signal; a switch signal generator coupled toat least the first detection component and configured to generate aswitch signal for controlling a switch for adjusting the input currentfor the power converter based on at least information associated withthe first comparison signal and the first detection signal; wherein: theswitch signal generator is further configured to generate the switchsignal to turn off the switch if the first comparison signal indicatesthe first signal is larger than the first threshold signal in magnitude;the switch signal generator is further configured to generate the switchsignal to turn off the switch if the first detection signal indicatesthe first signal is smaller than the second threshold signal inmagnitude.
 2. The system of claim 1, and further comprising: a seconddetection component configured to receive the first detection signal andoutput a second detection signal to the switch signal generator;wherein, if the first detection signal indicates the first signal issmaller than the second threshold signal in magnitude for apredetermined period of time, the second detection component is furtherconfigured to output the second detection signal causing the switch tobe shut down.
 3. The system of claim 1 wherein the second thresholdsignal is smaller than the first threshold signal in magnitude.
 4. Thesystem of claim 1 wherein the second threshold signal is a periodicsignal and increases from a first magnitude to a second magnitude withineach signal period.
 5. The system of claim 1 wherein the first detectioncomponent is further configured to receive a clock signal and detect thesecond comparison signal only if the clock signal is at one or morefalling edges.
 6. The system of claim 1 wherein the first detectioncomponent is further configured to receive a clock signal and detect thesecond comparison signal only if the clock signal is at one or morefalling edges or at a logic low level.
 7. The system of claim 1 whereinthe switch signal generator includes a pulse-width-modulation componentand a gate driver.
 8. The system of claim 7 wherein thepulse-width-modulation component includes a pulse-width-modulationcomparator and a logic controller.
 9. The system of claim 7 wherein: thepulse-width-modulation component is configured to receive at least thefirst comparison signal and the first detection signal and output amodulation signal to the gate driver; the gate driver is configured togenerate the switch signal based on at least information associated withthe modulation signal. 10.-24. (canceled)
 25. A method for protecting apower converter, the method comprising: receiving a first signal, afirst threshold signal, and a second threshold signal, the first signalbeing associated with an input current for a power converter, the secondthreshold signal being different from the first threshold signal inmagnitude; generating a first comparison signal based on at leastinformation associated with the first signal and the first thresholdsignal; generating a second comparison signal based on at leastinformation associated with the first signal and the second thresholdsignal; receiving the second comparison signal; detecting the secondcomparison signal only if one or more predetermined conditions aresatisfied; generating a first detection signal based on at leastinformation associated with the detected second comparison signal;processing information associated with the first comparison signal andthe first detection signal; generating a switch signal for controlling aswitch for adjusting the input current for the power converter based onat least information associated with the first comparison signal and thefirst detection signal; wherein the process for generating a switchsignal for controlling a switch includes: generating the switch signalto turn off the switch if the first comparison signal indicates thefirst signal is larger than the first threshold signal in magnitude;generating the switch signal to turn off the switch if the firstdetection signal indicates the first signal is smaller than the secondthreshold signal in magnitude.
 26. The method of claim 25, and furthercomprising: receiving the first detection signal; processing informationassociated with the first detection signal; if the first detectionsignal indicates the first signal is smaller than the second thresholdsignal in magnitude for a predetermined period of time, generating asecond detection signal causing the switch to be shut down.
 27. Themethod of claim 25 wherein the second threshold signal is smaller thanthe first threshold signal in magnitude.
 28. The method of claim 25wherein the second threshold signal is a periodic signal and increasesfrom a first magnitude to a second magnitude within each signal period.29. The method of claim 25, and further comprising: receiving a clocksignal; detecting the second comparison signal only if the clock signalis at one or more falling edges.
 30. The method of claim 25, and furthercomprising: receiving a clock signal; detecting the second comparisonsignal only if the clock signal is at one or more falling edges or at alogic low level. 31.-38. (canceled)